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Abstract
In 2025, Malaria continues to pose a significant global health threat, with Plasmodium falciparum responsible for the most severe and deadly cases. Despite the success of existing interventions, such as insecticide-treated bed nets, antimalarial drugs, and pre-erythrocytic vaccines (PEVs), these strategies have proven insufficient in interrupting parasite transmission within endemic populations. This persistent gap highlights the critical need for novel interventions such as transmission-blocking vaccines (TBVs), which target the sexual and mosquito stages of the parasite lifecycle to reduce community transmission of malaria. Among TBV candidates, Pfs230, a gamete surface protein, has emerged as a leading antigen. The first domain of the 14-domain cysteine-rich protein, referred to as Pfs230D1 has demonstrated favorable safety and immunogenicity profiles in Phase 1 and 2 clinical trials. Functional antibodies elicited by Pfs230D1 promote complement-mediated lysis of parasites in the mosquito midgut, attacking a developmental bottleneck when parasite levels are low by targeting surface proteins displayed in the mosquito midgut.
Functional antibody responses to TBVs are traditionally assessed using the mosquito-based Standard Membrane Feeding Assay (SMFA), which measures transmission-reducing activity (TRA) as the percent reduction in oocyst density. However, the SMFA is low-throughput biological assay that is logistically demanding, limiting its scalability for late-phase vaccine evaluation. To address these challenges, we developed P230Compete, a high-throughput, competitive ELISA platform that uses single-chain variable fragments to occlude functional epitopes on Pfs230D1 and quantify serum antibodies displaced from functional epitopes. Using serum from Pfs230D1-EPA/AS01 vaccinees (NCT02942277), we measured five features of antibodies that bound functional epitopes (F): total IgG (EUF), IgG subclasses (IgG1F, IgG3F, IgG4F), and complement-binding capacity (C1qF).
Logistic regression and receiver operating characteristic (ROC) analysis demonstrated that EUF and IgG1F were the strongest univariate predictors of high TRA (defined as >80%), with AUCs of 0.81 and 0.80 following the third vaccination, and 0.81 and 0.76 after the fourth. Combining EUF + IgG1F further improved predictive performance, yielding AUCs of 0.86 and 0.87, respectively. This work establishes P230Compete as a scalable, biologically grounded surrogate for SMFA. P230Compete enables rapid, quantitative assessment of functional antibody responses for use in TBV trials. Such an assay could be used in place of mosquito-based assays in late-stage trials and accelerate the TBV evaluation pipeline. Together, these findings position P230Compete and similar platforms to support development of TBV as critical components of multistage vaccine strategies for malaria elimination and eventual eradication.